1. Field of the Invention
The present invention pertains to apparatus for drilling oil and/or gas wells. In particular, it concerns portable well drilling units and special swivel apparatus designed therefor.
2. Description of the Prior Art
In conventional rotary drilling, a power driven rotary table operating through a so-called "Kelly joint" connected to the upper end of the drill pipe string is employed for rotating the drill string. High-powered drawwork systems, including derricks with multiple-strand, cable-connected crown and traveling blocks, are also employed for running the drill string into and out of the well and for otherwise performing drilling and pipe handling operations. Conventionally, the rotary table and the drawworks and the power units for driving and operating the same constitute massive, relatively, complicated and expensive structures, particularly those designed for deep drilling.
U.S. Pat. Nos. 3,722,603; 3,722,607 and 3,888,318 disclose fluid pressure operated snubber devices for use in drilling wells, which generally take the place of the rotary table and drawwork systems conventionally heretofore employed. The devices may comprise a stationary lower snubbing head and a rotatable and vertically reciprocable upper snubbing head for rotating drill pipe when drilling a well and for running the drill pipe into and out of the well. Other snubber devices are shown in U.S. Pat. Nos. 3,194,313 and 3,282,357.
Although other snubbing devices are known in the prior art, they are primarily for servicing operations, being used only to pull and rerun pipe in already completed wells. Such devices eliminate the need of killing the well and the cost, time and problems associated with circulating mud, salt water or other kill fluids. They also eliminate the danger of kill fluids causing permanent damage to the well bore and formation and the problem of loosing expensive kill fluids to the formation. However, such units have not heretofore been designed for, nor capable of, drilling.
One of the problems associated with snubbing devices suitable for drilling is the provision of a compatible swivel assembly which will not hinder the drilling operations. For example, the swivels of U.S. Pat. Nos. 3,194,313 and 3,282,357, disclose snubbing devices in which the swivel itself is used to deliver power for rotating the drill string. The swivel is threadedly engaged with the upper joint of the drill string. This arrangement calls for separate components for reciprocation of the drill string during running and pulling of the pipe and requires that the power swivel be removed during running in and pulling operations. Obviously, this increases operation time.